(1). Field of the Invention
The present invention relates generally to a rotary joint providing mechanical and electrical connection, and more particularly to a rotary joint between a rotating handling system or winch and a stationary structure.
(2) Description of the Prior Art
Current rotary joints used in handling arrays of hydrophones towed behind a vessel are found to be failing prematurely, i.e., failures have been observed after significantly shorter time periods than design life. Replacing failed rotary joints is costly and, in the case of a submarine towed array, replacement is made more difficult as the joint is located in the ballast tank of the submarine. The current rotary joints are seen to have a number of design problems.
The rotary joints contain pressurized insulating fluid within their cavities, tending to allow easier rotation of the shaft about the journal bearing of the joint. When the array is towed from a submarine at depth, the ballast tank becomes pressurized, putting external pressure on the joint, tending to collapse the joint and also increasing friction between the shaft and bearing. Thus, a pressure compensator is provided in the rotary joint to maintain the positive pressure within the joint cavity relative to the ballast tank. Current rotary joint pressure compensators consist of a neoprene bladder which becomes brittle and cracks after repeated temperature and pressure variations. The cracking allows seawater to infiltrate the rotary joint causing reduction in insulation resistance between the conductors. The towed array performance is thus degraded until at some point the seawater intrusion results in a complete electrical short. Also, the electrical contacts of current rotary joints are made of a material subject to flaking during use, allowing conductive material into the insulating fluid. As with seawater, this flaking leads to performance degradation and eventually to an electrical short.
In the rotary joints used in submarines, the present design makes high use of proprietary components and long lead items for manufacture which raises unit costs and extends fabrication times. Consequently, the inventory is kept at a minimum with resultant replacement delays when failures throughout the fleet exceed inventories. As noted previously, the location of the rotary joint in the ballast tank of submarines presents replacement difficulties. The weight and size of present rotary joints increase the difficulty. Further, there are presently four separate designs for the rotary joints used in navy vessels, thus further complicating inventory maintenance and replacement. in and not allowing quick replacement of units.